VOLUMETRICS OF ASPHALT MIX

OBJECT: DETERMINATION OF VOLUMETRICS OF ASPHALT MIX.

PERFORMANCE OBJECTIVE:

Upon successful completion of this lab experiment, students will be able to,

1. Perform sieve analysis tests on various aggregate stockpiles.
   
2. Select optimum proportions of different aggregate stockpiles that meet the design specification.
   

THEORY:

The intent of laboratory compaction is to simulate the in-place density of HMA after it has endured several years of traffic. It is necessary to understand the definitions and analytical procedures described here to be able to make informed decisions concerning the selection of the design asphalt mixture. The information here applies to both paving mixtures that have been compacted in the laboratory, and to undisturbed samples that have been removed from a pavement in the field.

Water Permeable Voids Not Filled

With Asphalt (Part of Aggregate

Volume for Effective S. G.)

Asphalt

Permeable

Voids (i. e. Absorbed

Aggregate

Air

Voids

Water Permeable Voids

(

Part of

Aggregate Volume of Bulk S. G., not

for Apparent S. G.)

Effective Asphalt

Binder

DEFINITIONS:

Bulk Specific Gravity, Gsb, – the ratio of the weight in air of a unit volume of permeable material (including both permeable and impermeable voids normal to the material) at a stated temperature to the weight in air of equal density of an equal volume of gas-free distilled water at a stated temperature. See Figure 10.1

Apparent Specific Gravity, G_sa – the ratio of the weight in air of a unit volume of an impermeable material at a stated temperature to the weight in air of equal density of an equal volume of gas free distilled water at a stated temperature. See Figure. 10.1

Fig 10.1

Effective Specific Gravity, G_se – the ratio of the weight in air of a unit volume of a permeable material (excluding voids permeable to asphalt) at a stated temperature to the weight in air of equal density of an equal volume of gas-free distilled water at a stated temperature. See Figure 10.1

PERCENT VMA IN COMPACTED PAVING MIXTURE:

The voids in the mineral aggregate, VMA, are defined as the intergranular void space between the aggregate particles in a compacted paving mixture that includes the air voids and the effective asphalt content, expressed as a percent of the total volume.

If the mix composition is determined as percent by weight of the total mixture:

Gmb = bulk specific gravity of compacted mixture.

Gsb = bulk specific gravity of total aggregate.

Pa = total percent of aggregate by total weight of the mixture.

PERCENT AIR VOIDS IN COMPACTED PAVING MIXTURE

The air voids, V_a, in the total compacted paving mixture, consist of the small air spaces between the coated aggregate particles. The volume percentage of air voids in a compacted mixture can be determined using:

Va = air voids in the compacted mixture, percent of the total volume

Gmm = maximum specific gravity of the paving mixture

PERCENT VFA IN COMPACTED PAVING MIXTURE

The voids filled with asphalt, VFA, is the percentage of the inter-granular void space between the aggregate particles (VMA) that are filled with asphalt. VFA, not including the absorbed asphalt, is determined using:

Prepare a separate graphical plot for these values and connect plotted points with a smooth curve that obtains the “best fit” for all values, as illustrated

Optimum bitumen content determination:

B1 = Bitumen content corresponding to maximum density =

B2 = Bitumen content corresponding to maximum Stability =

B3 = Bitumen content corresponding to 4% voids content =

OBC = Optimum bitumen content = (B1 + B2 + B3) / 3 =

COMMENTS: